Recently, multifunction and diversification of an electronic apparatus (particularly a portable terminal device, e.g., a cellular phone) have progressed, so that electroluminescent lamp (EL lamp) is used for illuminating a display area or an operating section of the apparatus.
A conventional electroluminescent lamp (EL lamp) will be described with reference to FIG. 6.
FIG. 6 shows a sectional view of the conventional EL lamp. As shown in FIG. 6, light-transmitting electrode-layer 52, e.g., indium tin oxide, is formed on a whole surface of transparent substrate 51, e.g., a glass or a film, using a sputtering method or an electron beam method.
The conventional EL lamp is formed by the following elements:
(a) luminescent layer 53 formed of the synthetic resin layer 53A in which phosphor particles 53B, e.g., zinc sulfide, (base material of luminescence) disperse, and formed on transparent substrate 51,
(b) dielectric layer 54 made of synthetic resin, where barium titanate disperses, and formed on luminescent layer 53,
(c) back electrode-layer 55 made of silver or carbon resin, and formed on dielectric layer 54, and
(d) insulating layer 56 made of epoxy resin or polyester resin and formed on back electrode-layer 55.
The EL lamp mentioned above is installed in an electronic apparatus, and an AC voltage is applied between light-transmitting electrode-layer 52 and back electrode-layer 55. As a result, phosphor particle 53B of luminescent layer 53 emits light, and the light illuminates a display area or an operating section of the electronic apparatus from behind.
Luminescent layer 53 is formed by the following method. First, paste is made of cyano resin or fluororubber dissolved in organic solvent. Second, phosphor particles 53B disperse in the paste. Third, the paste is formed by a reverse-roll coater or a die coater, or printed by a screen printing. Finally, the paste is dried and formed. By the coating method using the reverse-roll coater or the die coater, phosphor particles 53B can be dispersed in luminescent layer 53 uniformly to a certain extent by changing composition of phosphor particles 53B in the paste or thickness of the coating paste. By this coating method, the luminescent layer can coat on the whole surface of a rectangular substrate, however, can not coat the surface in a specific pattern.
When the specific pattern is required, the screen printing is usually used for forming luminescent layer 53. A screen mask used for the screen printing is made of sheet which is formed by knitting stainless threads or polyester threads of diameter approximately 30 xcexcm. The sheet is formed of opening-sections into which paste penetrates and closed-sections into which paste does not penetrate, so that a pattern of an electrode can be printed. As shown in FIG. 6, because the sheet is formed by knitting threads, area 53C under the threads or under intersections of the threads printed with phosphor particles 53B insufficiently or not printed tends to occur.
A mean diameter of phosphor particles 53B is approximately 20 xcexcm through 25 xcexcm. As shown in FIG. 6, when phosphor particles 53B are printed using a screen mask of thickness 60 xcexcm, two or three of phosphor particles 53B tends to pile up at an area 53D under the opening-section.
In the conventional EL lamp discussed above, phosphor particles 53B are difficult to disperse in luminescent layer 53 uniformly, so that an area on which phosphor particles 53B do not disperse or pile up tends to occur. As a result, light emission from phosphor particles 53B tends to produce uneven brightness.
When luminescent layer 53 is formed of paste, which is made of synthetic resin dissolved in organic solvent, and phosphor particles 53B disperse in the resin, a state of dispersing phosphor particles 53B tends to disperse unevenly even in the same printing condition. Because characteristics of printing is changed by diameters or shapes of phosphor particles 53B, or changed by a surface shape of light-transmitting electrode-layer 52.
The present invention addresses the problem discussed above, and aims to provide an electroluminescent lamp (EL lamp), of which brightness uniformity is improved, and provide a method for manufacturing the EL lamp.
The EL lamp of this invention includes the following elements:
(a) a transparent substrate,
(b) a light-transmitting electrode-layer formed on the transparent substrate,
(c) an adhesive synthetic resin layer formed on the light-transmitting electrode-layer,
(d) a luminescent layer which is formed of the synthetic resin layer with phosphor particles dispersed uniformly,
(e) a dielectric layer formed on the luminescent layer,
(d) a back electrode-layer formed on the dielectric layer.
Each phosphor particle disperses on the synthetic resin layer uniformly, and the luminescent layer is thus formed, so that the EL lamp having improved brightness uniformity is obtainable. Because a voltage is applied to the luminescent layer uniformly, an inexpensive and uniform EL lamp with high brightness using less phosphor particles is obtainable.
The method for manufacturing the EL lamp includes the following steps:
(a) forming a light-transmitting electrode-layer on a transparent substrate,
(b) forming an adhesive synthetic resin layer on the light-transmitting electrode-layer,
(c) sticking phosphor particles on the synthetic resin layer uniformly so that a luminescent layer is formed,
(d) forming a dielectric layer on the luminescent layer, and
(e) forming a back electrode-layer on the dielectric layer.
As a result, an inexpensive and uniform EL lamp having improved brightness can be produced.